DE4216189A1 - Material identification using spectroscopy and two laser light sources, e.g. for differentiation of human tissue - illuminating material with light at two wavelengths and determining intensity of luminescence or scattered light emitted from material in wavelength range below upper illuminating frequency - Google Patents

Abstract

The method involves illuminating the material to be identified with a frequency lambda 1, detecting the intensity of light emitted from the material between wavelengths lambda 2 and lambda 3, and comparing with values for known materials. The material (11) to be identified is additionally illuminated with the light of a fourth wavelength (lambda 4). This lies above the wavelength range of the second and third wavelengths (lambda 2 and lambda 3). Two lasers (7,8) are used as light sources and respectively produce light of first and fourth wavelengths (lambda 1 and 4). The light is fed into an optical waveguide (10) across a beam splitter (9) and led to the material being identified. The light emitted is fed across a second beam splitter (12) to an evaluator (13). USE/ADVANTAGE - For removing layers of dirt, lacquer, etc. without harming substrate material; cutting using stencil; medical applications, e.g. stone and tumour destruction, plaque removal from teeth. Clearer differentiation between materials of similar types.

Description

The invention relates to a method for material recognition by means of spectroscopy, in which the material to be identified is illuminated with light of a wavelength λ ₁ and the intensity of the luminescent and / or scattered light emitted by the material at at least one wavelength in a wavelength range between λ ₂ and λ ₃ is averaged and compared with previously determined values of known materials, the wavelength λ _{1 being} below the wavelength range λ ₂ to λ ₃ .

Material processing using laser light wins on numerous technical areas more and more important. Especially at this material processing, it is often necessary to ensure that only material I is processed, but not material II. For this is a quick and non-destructive material detection Requirement; Areas of application of such differ by material type There are numerous ornamental edits, for example here The following applications are listed: Removal of dirt and incrustations without damaging the base material, cutting or planar processing of materials along a template or a previously applied top coat, paint removal, medical Applications such as stone or tumor destruction,  removal of plaque from teeth, removal of deposits on vessels and the like. The above is only an example ten areas of application have the common characteristic that at the material processing by laser a high performance and Energy density in the work area is required on the one hand and others on the other hand, damage to the adjacent one not to be processed Material must be prevented by the laser light safely.

For the detection of materials, in particular material differentiation, a spectroscopy method is known which, due to the system, can be used particularly simply and inexpensively, in particular for such laser processing. Such a method is exemplified by DE 39 18 618 A1 or CC Hoyt and others "Remote Biomedical Spectroscopic Imaging of Human Artery Wall" in Laser Surg. Med. 1988; 8: 1-9 known. The methods described there work using fluorescence spectroscopy. The material to be identified in the working area of the processing laser is illuminated by light of a wavelength λ ₁ , either by the working laser itself or by an additional light source. The luminescence and / or scattered light emitted in this way is then analyzed in a wavelength range λ ₂ to λ ₃ at one or more wavelengths, the values determined being compared with previously determined values, in order in this way to recognize a specific material again. The wavelength λ _{1 of} the illuminating light is chosen so that it lies below the wavelength range λ ₂ to λ ₃ , that is to say that the wavelength λ _{1 is} less than λ ₂ . Depending on which material the device has identified, the high-energy processing laser is then released or blocked for (further) processing.

The method described above has proven itself in principle, comes across however to its limits where material can be seen, that is not  is completely homogeneous, in particular a high degree of dispersion in the has spectral distribution of the emitted light. This is common for biological material, e.g. B. human tissue, in plants or the like. Often it also applies to certain material Distinguish material groups in their spectral Lumi nescence or scattering properties are very similar.

Proceeding from this, the invention is based on the object Spectroscopic method for material detection of the type mentioned above so that a clearer mate rial differentiation is possible. Furthermore, a device is said to be ge create with which the method according to the invention apply can be detected.

The procedural part of the object is achieved according to the invention in that the material to be identified is additionally illuminated with light of a wavelength λ ₄ , the wavelength λ _{4 being} above the wavelength range determined by λ ₂ and λ ₄ , that is to say the wavelength λ _{4 is} larger than the wavelength λ ₃ . The device-related part of the task is solved by the features specified in claim 6. Advantageous embodiments of the invention are specified in the subclaims, the following description and the figures.

The illumination according to the invention of the material to be identified with light of a wavelength λ ₁ and additionally with light of a wavelength λ ₄ below or above the wavelength range determined by λ ₂ and λ ₄ has surprisingly shown that there are at least some materials, especially very similar ones Material groups sets a significantly more differentiated spectral distribution of the emitted light, which facilitates material detection. The differences in intensity within the selected spectral range are clearly spread compared to illumination with only one wavelength λ 1. The method according to the invention can also be used cheaply and simply, it is only necessary to ensure that light of wavelength λ _{4 is also} radiated in. This does not necessarily have to be laser light, the illuminating light only has to have a certain minimum intensity in the range of the wavelength λ ₁ and in the range of the wavelength λ ₄ , which can be determined empirically in the application. It is therefore not required for the invention to add coherent light or light exactly one wavelength. The method according to the invention can also be used in combination with the known material detection method, depending on the materials to be distinguished.

It has proven to be useful, but not for material detection the total intensity distribution of the emitted light over the to determine the specified wavelength range, but only to form characteristic values within this range as this is much easier and faster to carry out. Such a cha The simplest form of the characteristic value is the relative intensity of the emitted light at a detection wavelength within the Wavelength range.

A further differentiation can be achieved by first illuminating the material to be identified with light of wavelength λ ₁ and then illuminating it with light of wavelengths λ ₁ and λ ₄ - the order is irrelevant - with the relative intensity after each illumination process of the emitted light is measured at at least one detection wavelength within the wavelength range and then a characteristic value is formed from these intensity values obtained under different lighting by mathematical combination. In this refined method, the difference between the aforementioned recognition method and the recognition method according to the prior art is used in particular. The variance of the lighting can also consist in the different intensity of the light component with the wavelength λ ₄ .

It has proven itself in practice when in the wavelength spectrum of the emitted light is the relative intensity at two wavelengths determined within the previously specified wavelength range and these intensities are then related to each other , this ratio being a characteristic value for the material forms.

A further differentiation can be achieved by using the above-mentioned ratio formation once for the light emitted when illuminating with light of the wavelength λ ₁ and on the other hand when illuminating with light with the wavelengths λ ₁ and λ ₄ . Then the above-mentioned ratio and a further ratio arise, on the basis of the intensities resulting at two wavelengths after illumination with light of the wavelength λ ₁ . These two numbers determined by forming the quotient can in turn be related to one another, the number then resulting forming the characteristic value for material identification.

In order to carry out the method according to the invention, the known devices for material detection have to be modified since, on the one hand, an additional light source is required to generate light of wavelength λ ₄ and, on the other hand, this light of wavelength λ ₄ simultaneously with that of wavelength λ ₁ in the light guide or the optical system must be fed. Furthermore, it is necessary in particular for the differentiated detection methods described above that the light sources can be controlled individually. It is understood that the Auswertelek electronics is to be adapted accordingly, for example, to carry out the prescribed quotient formation and to be adapted to the two-stage process.

The invention is based on Darge in the drawings presented embodiments explained in more detail. Show it:

Fig. 1 shows a schematic representation of the relative Intensitätsver distributions of light emitted from a material at different irradiation light I,

Fig. 2 shows a diagram in illustration of FIG. 1 of another material,

Fig. 3 is a diagram showing the scattering of the characteristic values of two materials, once ermit telt by a method according to the prior art and another time determined according to the inventive method SEN,

Fig. 4 shows a schematic representation of the device structure for carrying out the detection method according to the invention and

Fig. 5 to 7 different pulse diagrams.

In Figs. 1 and 2, the spectral intensity distribution of the emitted light of elastin (Material I) and collagen (Material II) is shown schematically. Curve A shows the intensity distribution of the light emitted by elastin with simultaneous irradiation with light of the wavelength λ ₁ and with light of the wavelength λ ₄ . For comparison, the curve B is shown in Fig. 1, which shows the intensity distribution of the emitted light of the same material but when irradiated with light of wavelength λ ₄ . The drop in intensity in the upper wavelength range (near λ ₃ ) of curve A, which results from additional irradiation with light of wavelength λ _4, is clearly evident.

Corresponding curves for a material II, namely collagen, are entered in FIG. 2. Curves C and D are approximately identical, that is, collagen (material II), unlike elastin (material I), has approximately the same intensity distribution of the emitted light, regardless of whether with light of wavelength λ ₁ or additional is also irradiated with light of wavelength λ ₄ .

In the present case ( FIGS. 1 and 2), the wavelength λ _{1 is} 375 nm and the wavelength λ _{4 is} 750 nm. The wavelength range selected by filters lies between λ ₂ and λ ₃ . The wavelengths marked in broken lines in the figures within the wavelength range are 460 nm (number 1) and 530 nm (number 2 ).

If one looks at the curves B and D normalized in point 1 , which are based on excitation with light of wavelength λ ₁ (as is known from the prior art), it becomes clear that it is not possible to reliably differentiate the materials on the basis of these almost identical curves . On the other hand, if you compare the (also standardized) curves A and C, a clear difference is visible.

In order not to have to compare the spectral intensity distribution curves in their entirety over the wavelength range λ ₂ to λ ₃ , it is advisable to select one, two or more detection wavelengths 1,2 , to determine the relative intensity at these points and, if necessary, to mathematically determine the determined values to link with each other. In the present exemplary embodiment, the change in the spectra has been determined by the ratio of the relative intensities at two points 1 and 2 . I _B1 is the intensity at the detection wavelength 1, λ at the sole excitation by irradiation with light of the wavelength ₁ is obtained. I _B2 is the corresponding intensity at the detection wavelength 2 . The corresponding intensity values of curves A, C and D are numbered I _A1 , I _A2 , I _C1 , I _C2 and I _D1 , I _D2 . If the ratio V (V _A , V _B , V _C and V _D ) of the intensities is now formed for each pair of values 1, 2 , a material-characteristic value is obtained. Since the curves C and D ( FIG. 2) have a quasi-identical course, the same V values result for material II regardless of the excitation (the numerical values given come from practical experiments and are therefore not necessarily correct with the curve courses shown schematically in the figures match):

In contrast, the following values result for curves A and B in FIG. 1:

If one compares these characteristic values V _A -V _D , of which V _A and V _{B are} assigned to material I and V _C and V _D to material II, it becomes clear again that a distinction between the values V _B and V _D which result from excitations with light of wavelength λ ₁ is not possible or is extremely difficult, while the values V _A and V _C resulting from additional excitation with light of wavelength λ ₄ differ significantly from one another.

Further differentiation may take place by reacting the differences between the intensity distribution curves, when excited with light of wavelength λ ₁ with respect to the intensity distribution curves, when excited with light of wavelength λ ₁ and λ ₄ exploited. The following relationships then result, for example, as characteristic material parameters:

As the figures above make clear, this will make the Distinctiveness significantly increased again. This does not have to be be the same with all materials, but it can be done in a simple way be determined empirically.

Fig. 3 illustrates quite clearly that high significance provides the inventive method in material recognition. The point groups marked with the numbers 3 and 4 represent values which have resulted from numerous intensity value measurements on material I (number 3 ) and on material II (number 4 ) if these materials were only excited with light of the wavelength λ ₁ . Although there will be a statistical difference between the measuring point groups 3 and 4 , it cannot be ruled out that incorrect identifications will take place, as the overlapping measuring points of groups 3 and 4 show. If, on the other hand, the intensity of the same materials is measured when excited with light of wavelengths λ ₁ and λ _{4, a} measurement point distribution is obtained as indicated by the numbers 5 and 6 in FIG. 3. Here you can easily and reliably differentiate between materials I and II.

The aforementioned results are not limited to the specified wavelengths, they also result, for example, when λ _{4 is} not equal to twice the wavelength of λ ₁ . They can be used in particular for laser angioplasty, in which a healthy vascular wall is to be distinguished from sclerotic changes and an error detection can be excluded under all circumstances.

Fig. 4 shows the schematic structure of an apparatus for performing the method according to the invention, in particular for the application of Laserangiosplastie. In FIG. 4, 7 and 8 denote two lasers as light sources, on the one hand a dyelaser which generates light of the wavelength λ ₄ and on the other hand a HeCd laser which generates light of the wavelength λ ₁ . The light from these two lasers 7 , 8 is coupled into an optical waveguide 10 via a beam splitter 9 and directed onto the sample material 11 . The light emitted by the sample material 11 is fed back via the Lichtwellenlei ter 10 and transmitted via a second beam splitter 12 to an evaluation unit 13 which passes the wavelength range between λ ₂ and λ ₃ and then determines the intensity distribution at one or more detection wavelengths and, if necessary, the required mathematical relationships makes.

Instead of the second laser 8 , only the laser 7 with a subsequent doubling unit 14 can be used, the radiation splitter 9 can then be omitted. It can then be used to generate the wavelength λ _4, for example, an alexandrite laser as the laser 7 , whose light beam is divided, the partial beam of which is doubled in wavelength and finally combined with the other partial beam. Then there is a coupling into the optical waveguide 10 . The signal evaluation is the same as described above.

In both of the above-described embodiments, light of the wavelengths λ ₁ and / or the wavelength λ _{4 can} also be used for processing. In principle, the processing can also be carried out by a third processing wavelength λ ₄ , which is generated by the same or another laser.

Referring to Figs. 5 to 7 are shown three examples of time-varying lighting material. The diagrams marked with a show the switch-on time of the light source illuminating with the wavelength λ ₁ , the diagrams marked with b show the corresponding switch-on time of the light source radiating with λ ₄ and the diagrams marked with c show the characteristic ratio that results in the evaluation unit as an example.

In the example according to FIG. 5, light of the wavelengths λ ₁ and λ _{4 is} simultaneously directed onto the material to be recognized, the material recognition takes place approximately simultaneously, namely on the basis of the height of the V value. The V values for material I are shown in solid lines and those for material II in broken lines.

In the example according to FIG. 6, irradiation with light of the wavelengths λ ₁ takes place first and only after a certain time is irradiation with light of the wavelengths λ ₁ and λ ₄ . A significant difference in the materials is only visible after light of both wavelengths has been irradiated.

In the example according to FIG. 7, light with the wavelength λ _{1 is} continuously radiated in, while light with the wavelength λ ₄ is radiated in only for a time-limited interval. Corresponding is the course of the characteristic values, namely in a chronologically reverse order to that shown with reference to FIG. 6c.

Instead of switching on or off light of the wavelength λ ₄ , it is also conceivable to generate a significant difference between two or more materials by varying the irradiation intensity of the light of the wavelength λ ₄ .

Claims (7)

1. A method for material detection by means of spectroscopy, in which the material to be identified is illuminated with light of a wavelength λ ₁ and the intensity of the luminescent and / or scattered light emitted by the material is determined at at least one wavelength in a wavelength range between λ ₂ and λ ₃ and is compared with prior values of known materials, the wavelength λ _{1 being} below the wavelength range λ ₂ to λ ₄ , characterized in that the material to be identified is additionally illuminated with light of a wavelength λ ₄ , the wavelength λ ₄ above the by λ ₂ and λ ₃ specific wavelength range. 2. The method according to claim 1, characterized in that at least one characteristic value of the emitted luminescence and / or scattered light at at least one detection wavelength formed within the wavelength range for material detection becomes. 3. The method according to claim 1 or 2, characterized in that the material to be identified is successively illuminated with light of the wavelength λ ₁ and with light of the wavelengths λ ₁ and λ ₄ and the characteristic value using the differences resulting from the different illuminations is formed within the wavelength range in the emitted luminescent and / or scattered light. 4. The method according to any one of the preceding claims, characterized in that the material to be identified is simultaneously illuminated with light of the wavelengths λ ₁ and λ ₄ and then illuminated with light of the same wavelengths but with a different intensity of the wavelength λ ₄ and the characteristic value taking advantage of the differences in the different illuminations in the emitted luminescent and / or scattered light is formed within the wavelength range. 5. The method according to any one of the preceding claims, characterized characterized in that the characteristic value of the emitted Lumi nescent and / or scattered light the ratio V of the relative intensi would do at least two wavelengths within the wavelength is formed. 6. The method according to any one of the preceding claims, characterized in that the material to be identified is _first illuminated with light of the wavelength λ ₁ and the ratio V _{1 of} the relative intensities at two wavelengths within the wavelength range is formed on the basis of the emitted luminescence and / or scattered light is, after which the material to be identified is additionally illuminated with light of a wavelength λ ₄ and then again based on the emitted luminescence and / or scattered light the ratio V _{2 of} the relative intensities at the same wavelengths as before, which is characterized by this two ratios resulting values V ₁ and V ₂ to each other in the ratio V _{12 are} set and form a characteristic value V ₁₂ for material identification. 7. Device for material detection by means of spectroscopy, in particular for carrying out the method according to one of the preceding claims, with a light source for generating light of wavelength λ ₁ and with a detector for determining the intensity of the luminescent and / or scattered light emitted by the irradiated material at least one wavelength, with a filter device connected upstream of the detector, which passes at least one selected wavelength into a wavelength range from λ ₂ to λ ₃ above λ ₁ , and with evaluation electronics, characterized in that a light source for generating light Wavelength λ _{4 is} provided, the wavelength λ _{4 being} above half the wavelength range λ ₂ to λ ₃ .